title: Lytic bacteriophages reduce Escherichia coli O157: H7 on fresh cut lettuce introduced through cross-contamination.
abstract: The role of lytic bacteriophages in preventing cross contamination of produce has not been evaluated. A cocktail of three lytic phages specific forE. coliO157:H7 (EcoShield™) or a control (phosphate buffered saline, PBS) was applied to lettuce by either; (1) immersion of lettuce in 500 ml of EcoShield™ 8.3 log PFU/ml or 9.8 log PFU/ml for up to 2 min before inoculation withE. coliO157:H7; (2) spray-application of EcoShield™ (9.3 log PFU/ml) to lettuce after inoculation withE. coliO157:H7 (4.10 CFU/cm2) following exposure to 50 μg/ml chlorine for 30 sec. After immersion studies, lettuce was spot-inoculated withE. coliO157:H7 (2.38 CFU/cm2). Phage-treated, inoculated lettuce pieces were stored at 4°C for and analyzed forE. coliO157:H7 populations for up to 7 d. Immersion of lettuce in 9.8 log PFU/ml EcoShield™ for 2 min significantly (p < 0.05) reducedE. coliO157:H7 populations after 24 h when stored at 4°C compared with controls. Immersion of lettuce in suspensions containing high concentrations of EcoShield™ (9.8 log PFU/ml) resulted in the deposition of high concentrations (7.8 log log PFU/cm2) of bacteriophages on the surface of fresh cut lettuce, potentially contributing to the efficacy of the lytic phages on lettuce. Spraying phages on to inoculated fresh cut lettuce after being washed in hypochlorite solution was significantly more effective in reducingE. coliO157:H7 populations (2.22 log CFU/cm2) on day 0 compared with control treatments (4.10 log CFU/cm2). Both immersion and spray treatments provided protection fromE. coliO157:H7 contamination on lettuce, but spray application of lytic bacteriophages to lettuce was more effective in immediately reducingE. coliO157:H7 populations fresh cut lettuce.
authors.affiliation: United States Department of Agriculture; Agricultural Research Service; Environmental Microbial and Food Safety Laboratory; Henry A Wallace Beltsville Agricultural Research Center; Beltsville, MD USA.
authors.forename: Sean
authors.initials: S
authors.lastname: Ferguson
authors.forename: Cheryl
authors.initials: C
authors.lastname: Roberts
authors.forename: Eric
authors.initials: E
authors.lastname: Handy
authors.forename: Manan
authors.initials: M
authors.lastname: Sharma
keywords: E. coli  O157:H7; bacteriophages; lettuce; processing